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Spectrophotometric data of the young planetary nebula M 3-27, from 2004 to 2021, are presented and discussed. We corroborate that the H  i Balmer lines present features indicating they are emitted by the central star, therefore He  i lines were used to correct line fluxes by effects of reddening. Important variability on the nebular emission lines between 1964 and 2021, probably related to density changes in the nebula, is reported. Diagnostic diagrams to derive electron temperatures and densities have been constructed. The nebula shows a very large density contrast with an inner density of the order of 107 cm−3 and an outer density of about 103–104 cm−3. With these values of density, electron temperatures of 16 000–18 000 K have been found from collisionally excited lines. Because the central star emits in the H+ lines, ionic abundances relative to He+ were calculated from collisionally excited and recombination lines, and scaled to H+ by considering that He+/H+ = He/H = 0.11. Abundance discrepancy factor (O+2) values were also determined. Total abundance values obtained indicate sub-solar abundances, similar to what is found in other comparable objects like IC 4997. [ABSTRACT FROM AUTHOR]

From high-resolution spectra, chemical abundances from collisionally excited lines (CELs) and optical recombination lines (ORLs) have been determined for planetary nebulae (PNe) Cn 3-1, Vy 2-2, Hu 2-1, Vy 1-2 and IC 4997, which are young and dense objects. The main aim of this work is to derive their O+2/H+ abundance discrepancy factors (ADFs) between CELs and ORLs. He, O, N, Ne, Ar, S, and Cl abundances were obtained and our values are in agreement with those previously reported. We found that Cn 3-1, Hu 2-1, and Vy 1-2 have O abundances typical of disc PNe, while Vy 2-2 and IC 4997 are low O abundance objects (⁠|$\rm {12+log(O/H) \sim 8.2}$|⁠), which can be attributed to possible O depletion into dust grains. ADFs(O+2) of |$4.30^{+1.00}_{-1.16}$|⁠ , 1.85 ± 1.05, |$5.34^{+1.27}_{-1.08}$| and |$4.87^{+4.34}_{-2.71}$| were determined for Vy 2-2, Hu 2-1, Vy 1-2, and IC 4997, respectively. The kinematics of CELs and ORLs was analysed for each case to study the possibility that different coexisting plasmas in the nebula emit them. Expansion velocities of [O  iii ] and O  ii are equal within uncertainties in three PNe, providing no evidence for these lines being emitted in different zones. Exceptions are Hu 2-1 and Vy 2-2, where ORLs might be emitted in different zones than CELs. For Vy 2-2 and IC 4997, we found that nebular and auroral lines of the same ion (S+, N+, Ar+2, Ar+3, O+2) might present different expansion velocities. Auroral lines show lower |$\rm {V_{exp}}$|⁠ , which might indicate that they are emitted in a denser and inner zone than the nebular ones. [ABSTRACT FROM AUTHOR]

We present chemical abundance determinations of two H  ii regions in the dwarf irregular (dIrr) galaxy Leo A from Gran Telescopio Canarias (GTC) Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) long-slit spectra. Both H  ii regions are of low excitation and seem to be ionized by stars later than O8V spectral type. In one of the H  ii regions we used the direct method: O+2 ionic abundance was calculated using an electronic temperature determined from the [O  iii ] λλ4363/5007 line ratio; ionic abundances of O+, N+, and S+ were calculated using a temperature derived from a parametrized formula. O, N, and S total abundances were calculated using ionization correction factors from the literature for each element. Chemical abundances using strong-line methods were also determined, with similar results. For the second H  ii region, no electron temperature was determined thus the direct method cannot be used. We computed photoionization structure models for both H  ii regions in order to determine their chemical composition from the best-fitting models. It is confirmed that Leo A in a very low metallicity galaxy, with 12 + log(O/H) = 7.4 ± 0.2, log(N/O) = −1.6, and log(S/O) = −1.1. Emission lines of the only planetary nebula (PN) detected in Leo A were re-analysed and a photoionization model was computed. This PN shows 12 + log(O/H) very similar to the ones of the H  ii regions and a low N abundance, although its log(N/O) ratio is much larger than the values of the H  ii regions. Its central star seems to have had an initial mass lower than 2 M⊙. [ABSTRACT FROM AUTHOR]

The kinematics of the plasma in 14 planetary nebulae (PNe) is analysed by measuring the expansion velocities (Vexp) of different ions as derived from their collisionally excited lines (CELs) and optical recombination lines (ORLs). Vexp is analysed as a function of the ionization potential of ions, which at a first approximation represents the distance of the ion from the central star. In most cases, the kinematics of ORLs is incompatible with the kinematics of CELs at the same ionization potential, especially if CELs and ORLs are considered for the same ion. In general, Vexp from ORLs is lower than Vexp from CELs, indicating that, if the gas is in ionization equilibrium, ORLs are emitted by a gas located closer to the central star. The velocity field derived from CELs shows a gradient accelerating outwards as predicted from hydrodynamic modelling of PNe ionization structures. The velocity field derived from ORLs is different. In many cases, the velocity gradient is flatter or non-existent and highly and lowly ionized species present nearly the same Vexp. In addition, the full width at half-maximum (FWHM) for ORLs is usually smaller than FWHM(CEL). Our interpretation is that ORLs are mainly emitted by a plasma that coexists with the plasma emitting CELs, but does not fit the ionization structures predicted by models. Such a plasma should have been ejected in a different event from the plasma emitting CELs. [ABSTRACT FROM AUTHOR]

The spectroscopic evolution of Hen 3-1357, the Stingray Nebula, is presented by analysing data from 1990 to 2021. High-resolution data obtained in 2021 with South African Large Telescope High Resolution Spectrograph and in 2009 with European Southern Observatory-Very Large Telescope UVES spectrograph are used to determine physical conditions and chemical abundances in the nebula. From comparison of these data with data from different epochs it is found that the intensity of highly ionized emission lines has been decreasing with time, while the emission of low-ionization lines has been increasing, confirming that the nebula is recombining, lowering its excitation class, as a consequence of the changes in the central star which in 2002 had an effective temperature of 60 000 K and from then it has been getting colder. The present effective temperature of the central star is about 40 000 K. It has been suggested that the central star has suffered a late thermal pulse and it is returning to the AGB phase. The nebular chemistry of Hen 3-1357 indicates that all the elements, except He and Ne, present subsolar abundances. The comparison of the nebular abundances with the values predicted by stellar nucleosynthesis models at the end of the AGB phase shows that the central star had an initial mass lower than 1.5 M⊙. We estimated the ADF(O+2) to be between 2.6 and 3.5. [ABSTRACT FROM AUTHOR]

The analysis of 20 yr of spectrophotometric data of the double-shell planetary nebula (PN) PM 1-188 is presented, aiming to determine the time evolution of the emission lines and the physical conditions of the nebula, as a consequence of the systematic fading of its [WC 10] central star whose brightness has declined by about 10 mag in the past 40 yr. Our main results include that the [O  iii ], [O  ii ], and [N  ii ] line intensities are increasing with time in the inner nebula as a consequence of an increase in electron temperature from 11 000 K in 2005 to more than 14 000 K in 2018, due to shocks. The intensities of the same lines are decreasing in the outer nebula, due to a decrease in temperature, from 13 000 to 7000 K, in the same period. The chemical compositions of the inner and outer shells are derived and they are similar. Both nebulae present subsolar O, S, and Ar abundances, while they are He, N, and Ne rich. For the outer nebula, the values are 12 + log He/H = 11.13 ± 0.05, 12 + log O/H = 8.04 ± 0.04, 12 + log N/H = 7.87 ± 0.06, 12 + log S/H = 7.18 ± 0.10, and 12 + log Ar = 5.33 ± 0.16. The O, S, and Ar abundances are several times lower than the average values found in disc non-Type I PNe, and are reminiscent of some halo PNe. From high-resolution spectra, an outflow in the N–S direction was found in the inner zone. Position–velocity diagrams show that the outflow expands at velocities in the −150 to 100 km s−1 range, and both shells have expansion velocities of about 40 km s−1. [ABSTRACT FROM AUTHOR]